Just trying to understand. Accepting the premise that there are only two methods of acquiring citizenship (1. being born "in" the United States and 2. naturalization "in" the United States), does a person born "outside" the United States to a United States citizen acquire citizenship through birth or naturalization?
It depends upon their parentage. Federal laws have defined who is and is not born a citizen over the last 225 years, but especially in the early years it was based on English Common Law which held that citizenship by birth occurred when a child was born in the country or territories of the country, or when born to parents who were citizens themselves.
If a child does not have to be naturalized, as determined by the law, then they are citizens by birth.
My grandson was born in London to an English mother and a US Citizen father. His American passport as a US citizen was issued that day as he was a US Citizen at the moment of his birth. (He is also an English citizen.) That is the same exact situation as Cruz's birth. He was born to a US Citizen in Canada so he was a US citizen the moment of his birth. Neither Cruz nor my grandson had to be naturalized as they were US Citizens the moment they were born.